Navigational apparatus

ABSTRACT

Navigational apparatus comprises a primary hazard sensor, for example a weather radar, for providing signals representing the distribution of hazards ahead of a moving vehicle, connected to a computer. The computer is programmed to compute at least one path substantially avoiding the hazards. An indicator may be connected to an output of the computer to display the paths computed in relation to the hazards. The vehicle guidance system may also be controlled by the computer output so that the vehicle follows one of the computed paths. The computer may be programmed to consider a number of possible paths through a given hazard distribution and to select advantageous paths from those considered for display together with an indication of the risk and economy of each selected path.

llnited States Patent Britland et a1.

[ 1 NAVIGATIONAL APPARATUS [75] Inventors: Colin Morris Britland,Bagshot;

John Bernard Joseph Thorpe, Ash, both of England [73] Assignee: TheSecretary of State for Defense in Her Britannic Majestys Government ofthe United Kingdom of Great Britain and Northern Ireland, London,England [22] Filed: Apr. 3, 1972 21 Appl. No.: 240,406

[52] US. Cl 235/l50.26, 343/5 DP, 343/5 W,

343/7 TA, 343/112 CA [51] Int. Cl. G06f 15/50 [58] Field of Search235/l50.23, 150.26;

343/5 DP, 5 W, 7 TA, 112 CA; 444/1 [5 6] References Cited UNITED STATESPATENTS 3,359,557 12/1967 Fow et a]. 343/5 W 3,310,806 3/1967 Stansbury235/150.23 X

Primary Examiner-Malcolm A. Morrison Assistant ExaminerR. StephenDildine, Jr. Atzorney-Moore & Hall 5 7] ABSTRACT Navigational apparatuscomprises a primary hazard sensor, for example a weather radar, forproviding signals representing the distribution of hazards ahead of amoving vehicle, connected to a computer. The computer is programmed tocompute at least one path substantially avoiding the hazards. Anindicator may be connected to an output of the computer to display thepaths computed in relation to the hazards. The vehicle guidance systemmay also be controlled by the computer output so that the vehiclefollows one of the computed paths. The computer may be programmed toconsider a number of possible paths through a given hazard distributionand to select advantageous paths from those considered for displaytogether with an indication of the risk and economy of each selectedpath.

8 Claims, 8 Drawing Figures s. A. r. K9

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PATENTED DEC 2 5 I975 sum 8 a; 3

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BACKGROUND OF THE INVENTION This invention relates to navigationalapparatus and in particular to navigational apparatus for providinginformation for the automatically or manually controlled safe navigationthrough groups of hazards with minimum detours. In a ship-borneapplication of the invention these hazards might be land masses, rocks,wrecks, or other moored ships and in an airborne application they mightbe stormy areas, or, in low level flight, terrestial obstacles.

In known navigational apparatus information from primary sensors such asradar or sonar carried on a vehicle to be controlled is presentedvisually to a pilot/- helmsman (hereinafter referred to as the driver)of the vehicle for example on a cathode-ray oscilloscope screen. Theinformation depicted on the screen indicates the real-time presence ofhazards and other navigational features in relation to the drivers ownvehicle position. With such a presentation the driver can decide thefuture course, for example the safest and/or the quickest course, forhis vehicle and cause it to follow that course by suitable movement ofthe vehicles primary controls. The decision process is repeatedconstantly throughout the voyage and being a subjective process thedecisions taken are not always correct and are certainly not always theoptimum choice with respect to safety and/or economy. Because of themany other duties that the present day driver has to perform, forexample communicating with bases and other vehicles and monitoring anever increasing number of displays indicating various aspects of thevehicles performance, the time available to him for this decisionprocess is short. This is especially true for the pilot of a passengercarrying aircraft flying at supersonic speeds in which the decision asto the most advisable flight path, through or around a pattern ofhazardous storm centers indicated by the weather radar as being even upto 300Km ahead, must be made extremely rapidly, bearing in mind thatwith the manoeuvres allowed, consistent with passenger comfort, alateral displacement of say 30Km from the desired course may have to beinitiated some lO-l5OKm further back.

SUMMARY OF THE INVENTION It is an object of the present invention toassist the driver by presenting him at suitable time intervals with asimple choice of one or a few preferred paths towards a givendestination, with an indication of the degree of hazard or penaltyassociated with each choice.

According to the present invention navigational apparatus for use in amoving vehicle comprises a hazard indicating apparatus constructed toprovide signals representing the location of hazards with respect to theposition of the hazard indicating apparatus, and a computer connected toreceive the said signals from the hazard indicating apparatus andprogrammed to compute parameters of at least one path substantiallyavoiding the hazards and to provide signal outputs representing thecomputed parameters.

In the present specification the term vehicle should be interpretedwidely, to mean any apparatus for the transport of goods or people onland or sea or in the air.

For instance the computer may be arranged to compute the parameters ofthe most economical path involving a negligible risk and the mosteconomical path involving a tolerable risk.

The computer may also be adapted for connection to one or morenavigational displays and the signal outputs therefrom may be adapted toindicate on the said displays the parameters of the paths computed orthe paths represented thereby.

The computer may also, or alternatively be adapted for connection to thecontrol system of the vehicle and the signal outputs therefrom may beadapted to operate on the system so as to cause the vehicle to follow aselected one of the paths computed.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention willnow be described by way of example only and with reference to theaccompanying drawings of which,

FIG. 1 is a schematic circuit diagram of an airborne storm avoidancenavigational apparatus,

FIG. 2 is a diagrammatic representation of some of the possible flightpaths considered by the apparatus of FIG. 1,

FIGS. 3, 3a, and 3b comprise a flow chart showing the manner in whichthe apparatus of FIG. 1 considers the possible paths through a stormpattern and FIGS. 4, 4a, and 4b comprise a flow chart showing the mannerin which the apparatus of FIG. 1 considers the possible paths through astorm pattern taking into account the effect of the wind speed anddirection in the region of the storms forming that pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an airborne stormavoidance navigational apparatus installed in an aircraft (not shown),comprises a weather radar set 1 connected to an antenna 2. The radar set1 has electrical outputs 3 and 4 connected to supply storm range andbearing signals respectively to two inputs R and 6 of an electroniccomputer 8. A manually operated windspeed and wind direction selector 9is connected to two further inputs W and W of the computer 8. Thecomputer 8 has outputs 10 and 11 each connected to a separate one of twoinputs of both a navigational display 12 and a weather radar display 13.Switches 14 and 17 enable one of the outputs 10 or 11 to be furtherconnected to a flight director 15 or to an auto-pilot 16. The weatherradar display 13 also receives signals from the outputs 3 and 4 of theradar set 1.

At intervals during the flight of the aircraft an operator sets thewindspeed and wind direction selector 9 to the best estimated value ofthe windspeed and wind direction at the aircrafts height in an azimuthalsector of interest ahead of the aircraft and scanned by the antenna 2.This selection causes a corresponding pair of electrical signals,representing these variables to be fed to the inputs W and W of thecomputer 8. Radar signals are transmitted and received by the radar set1 through the antenna 2. The received signals are processed to produceelectrical signals representing the range and bearing of storm centersof intensity greater than a certain (possibly adjustable) intensity,within the sector of interest. These signals are normally fed continuously from the outputs 3 and 4 of the radar set 1 to the weatherradar display 13. In the present apparatus sets of these signalsrepresenting the storm pattern at a given instant of time are also fedat suitable time intervals to the R and 6 inputs of the computer 8.

Firstly the computer reads the coordinates of the hazards (stormcenters) detected by the weather radar 1. These are given by range (R)and bearing (6) signals relative to the present position and presentheading of the aircraft. For convenience of calculation, the computerderives the corresponding cartesian coordinates for the storm centers,relative to a cartesian coordinate system with orthogonal x and y axes,having its origin at the present position of the aircraft. This can bedone by a conventional subroutine. It may be desirable to include acorrection, dependent on the aircrafts present heading and positionrelative to the desired track, to incline the y axis of the cartesiancoordinate system towards the desired flight direction, even if theaircraft has turned in the course of a detour around some hazard. Thiscorrection requires an extra input #1,, representing the aircraftspresent heading relative to the direction of the track, which can beobtained from a conventional direction-finding or navigation apparatus(not shown). The derived cartesian coordinates of the storm centers arestored in a logical order, according to their range from the aircraft.

The computer 8 is programmed to consider a finite number of possiblealternative paths through the storm pattern presented to it at any time,each formed of a predetermined number of successive arcuate segments ofequal length. It is assumed that, at the beginning of each segment, anyone of a finite predetermined selection of alternative manoeuvres can bebegun and maintained until the end of the segment is reached, afterwhich the same range of alternative manoeuvres can again be consideredfor the following segment. Typically each segment may be flown using anyone of the following five possible alternative manoeuvres or arcs:

i. 10 right bank ii. right bank iii. substantially straight and levelflight iv. 5 left bank v. left bank The first step in the pathassessment programme examines one out of the five possible arcs startingfrom the present position of the aircraft, and each subsequent stepexamines one out of the five possible arcs starting from the end of thepreceding arc. Paths of four segments; each involving four successivearcs are considered. Some of the possible flight paths defined by a fivechoice, four segment path investigation are illustrated in FIG. 2. Thepoints 18 represent the positions that would be arrived at if each ofthe five alternative manoeuvres of the first segment, starting from theaircrafts present position 17, was followed. The points 19 represent theends of some of the twenty five possible arcs defining the secondsegments; points 20 represent the ends of some of the one hundred andtwenty five possible arcs defining the third segments; and the points 21represent some of the ends of the six hundred and twenty five possiblearcs defining the fourth segments. For clarity only three of thecomplete family of possible paths are shown. These are paths 22, 23 and24. The path 22 consists of four similar straight ahead segments. Inpath 23 the first segment is covered by a 5 right bank from the startingposition 17; the second segment is straight and the third segment is a10 right bank and the fourth segment is a 10 left bank. In path 24 thefirst segment is a 5 left bank, the second and third segments are 5right banks and the fourth segment, is a 10 right bank. The paths 23 and24 would be completed, in the computation, by appropriate manoeuvres tobring the aircraft back to the desired track. These manoeuvres are shownby broken curves on FIG. 2.

The number of segments considered, and the number of alternativemanoeuvres reviewed at the beginning of each segment, are clearlyarbitrary. To make the following description more general, the number ofsegments in each path will be called s and the number of alternativemanoeuvres reviewed at each decision will be called n. Each path willthen be associated with, and defined by, a set of parameters 0,, a a,which represent the manoeuvres selected for examination at the beginningof successive segments along the path. In general a, will represent themanoeuvre selected for examination at the beginning of the rth segment.The parameters a, will have integral values less than or equal to n, andthe total number of paths to be considered will be n. For instance theparameters a, may have values l to 5 corresponding to the choices (i) to(v) hereinbefore listed.

The computer programme is arranged to investigate the possible paths ina logical order; for various reasons some paths may be eliminated fromfurther consideration at an early stage in their consideration; whenevera path is so rejected, or when a path has been fully investigated, theprogramme turns to a consideration of the next possible path in thelogical order, until all possible paths have been either rejected orinvestigated. Hazard scores, for example related to the proximity of thepath to detected storm centers or other hazards, and penalty scores forexample indicating the length of any detour involved, the lateraldeviation from the desired track or the number of bank reversals, areobtained in the process for each fully investigated path. At thecompletion of the process the computer selects details of some of themost advantageous paths, for instance the shortest path having anegligible hazard score and the shortest path having a hazard score notgreater than a predetermined score which is deemed tolerable. Theparameters determining the hazard scores and the penalty scores will ingeneral be defined by the aircraft operators and the air safetyauthorities. Electrical signals representing these selected paths arethen fed from the computer outputs, such as 10 and 11 and may besuperimposed on the navigational and weather radar displays 12 and 13.The pilot or operator can then select one of these paths by means of theswitches 14 and 17 to show the path to be followed on the flightdirector 15 for the pilot to steer, or to feed the path directions tothe auto-pilot 16 which may then automatically steer the aircraft alongthat path, when the auto-pilot is allowed to control the aircraft.

The hazard score which will be calculated for any arc underconsideration is a numerical quantity which must depend in a chosenpredetermined way on the proximity of the arc to the adjacent stormcenters. For instance the hazard score may be determined by summingcontributions each calculated as a predetermined function of the nearestdistance from a given storm center to a point on the arc; eachcontribution may, for instance, be a linear function of distance fromthe edge of a forbidden zone, or an inverse function of the shortestradial distance from the storm center, or a function of the distancetravelled on parts of the path within a predetermined range fromthe'storm center. The hazard score calculations may take account of anysignificant effects of the prevailing wind speed and wind direction (asfed into inputs W and W) on the hazard involved in the proximity to astorm, for example any expected downwind turbulence which may not berevealed on the radar display 13.

Specified temporary store locations are allocated to the parameters 11,,a a The programme starts with the parameters a, a a a 0 as shown by BoxA of FIG. 3 indicating that no manoeuvre has yet been selected forexamination.

FIG. 3 (including FIGS. 3a and 3b) illustrates the search and decisionprocess that enables the computer to select the most economicalhazard-free path and the most economical acceptable risk path from the npossible paths available. The various boxes, A, B, C, etc shown in FIG.'3 represent computer operations that will take place when a certainresult is obtained from a previous operation. At the starting point ofeach segment of a path, there are three essential values which arerelevant to the subsequent calculations, namely the x coordinate, the ycoordinate, and the direction of the path at that point. The symbols X,,Y, and (I), will hereinafter'be used to indicate the x, y and directioncoordinates at the finish of the rth segment of a path underconsideration. Analogously, the symbols X,,, Y and 4),, will be used toindicate the initial position and heading of the aircraft, which is thestarting point for the first segment of all the paths, at the start ofeach computer cycle. To make the following description equallyapplicable to the consideration of the second or any subsequent segmentof a path, the coordinates of the starting point of the segment will berepresented by X,.,, Y, and

A set of store addresses, hereinafter referred to as the SPCstores, areallocated for storing the starting point coordinates of the segments ofthe path under consideration. Since at least several of the paths to beconsidered will probably have s segments, there are s SPC stores. Theinitial position coordinates X Y (b will be stored in the first SPCstore. As hereinbefore indicated, the current values of the parameters aa a a, will indicate the path and the path segment under considerationat any stage. The process hereinafter described will ensure that whenthe rth segment of any path is being considered, the first, second rthSPC stores will hold the starting point coordinates of thefirst,-second, rth segments respectively of that path.

As hereinbefore described with reference to Box A, the storm center datais first converted and stored in a form suitable for the computer to usein the path selection process, and the parameters a, set to zero. In thefirst step of the process proper, indicated by box B in FIG. 3, thestarting point coordinates (X, Y, 15,.,) of the segment to be consideredare taken from the rth SPC store, where r is the ordinal number (suffix)of the first zero valued parameter in the set 0 a a The set of stormcenter coordinates is then examined with reference to the startingpoint, to see if there are any storms within a predetermined distance ofthe most direct path from the starting point to the desired track; ifthere are none the most direct path will be chosen im- "mediately andthere will be no need to investigate the alternative possibilities; inthis case the next operation is indicated by box 1. If there are somestorms in the area around the most direct path between the startingpoint and the desired track, the next operation is indicated by box C,where the computer revises the set of parameters a a a, to indicate thesegment which is about to be investigated. To do this it adds one to thefirst zero-valued parameter of the set when examined in the order a a a3 a or if all the parameters have non-zero values, it adds one to thelast parameter a,. If this makes a, equal to n 1, then it resets a, tozero and adds one to the preceding parameter a, If this makes a equal ton 1, it resets a, to zero and adds one to the preceding parameter; carryactions of this kind can continue back to a When this process returnsall the parameters to zero, all the paths have been considered. Thecomputer uses this latter condition as indicated by Box D, to determinewhether its next operation is to be as indicated by Box E or Box L.

When the set of parameters has been revised in this way, and assumingall the parameters a, are not zero, the position and value of the lastnon-zero parameter indicate the position of the segment and themanoeuvre under consideration for that segment. For instance, when 11,,a a, have non-zero values and a a .=a,= O, the segment to be consideredis the rth segment of an incomplete path defined by the successivemanoeuvres indicated by a a .a,.. To give a specific example, if the setof parameters was 2,3,1 ,0, the programme would be about to consider theeffect of a 10 right bank (a l during the third segment of the path 23on FIG. 2.

In the next operation (if the process is not finished), represented bybox E, the coordinates of the starting point are taken from the SPCstore corresponding to the last non zero path parameter of the revisedparameters. These coordinates and the nature of the manoeuvre (indicatedby the value of a,.) are used to calculate the coordinates (X,, Y,, ofthe end point of the segment, according to the equations r r-l r bf-lSin br-l r r-l (ch-1 C08 d r-1) Where (1) K/La,., K is the segmentlength which as hereinbefore described is a fixed value for allmanoeuvres in this example, and La is the radius of turn of themanoeuvre currently under consideration for the rth segment, and thesecoordinates are stored in the (r l)th SPC store. Next, as indicated bybox F, they are compared with prescribed arbitrary limits of maximumacceptable heading deviation (mod d), limit) and maximum acceptablelateral deviation (mod X, limit) and with the storm coordinate list. Ifthe end point coordinates indicate an excessive deviation from the mostdirect route, or that the end point will be unacceptably close to astorm, the next action indicated by box K will be to change the pathunder consideration.

However if the end point is acceptable, ith respect to all three limitconsiderations the next operation will be as indicated by box G. In boxG the computer selects from all the storm center coordinates thosestorms lying within a predetermined area around the segment underconsideration, and computes the hazard contribution of each of theselected storms, to the hazard score for that segment. The hazardcontribution is a number, calculated according to a predeterminedfunction of the distance of approach of the segment to a selected stormcenter. The hazard contributions of all the selected storms are thensummed'to obtain a hazard score for the segment.

If this score exceeds a prescribed limit, the parameters a a, arerevised by the action represented in box K. This action which may beinitiated by rejection of an unacceptable manoeuvre either in the actionof box F or box G, adds one to the value of a, (the last non-zeroparameter, which represents the manoeuvre resulting in the excessivehazard score). If this makes a, n I, it generates a carry actionresetting a, to zero and adding one to the preceding parameter a, andsimilar carry actions may be propagated to earlier parameters as in theupdating procedure in box C as hereinbefore described. This actioneffectively rejects the excessively hazardous manoeuvre and all furtherpaths leading from it, and advances the selection process to aconsideration of the next alternative, restarting the process at box E(unless, of course, the computer decides in box D that the process isthen completed).

On the other hand, if the hazard score does not exceed the prescribedlimit, the next operation is to store the hazard score as indicated inbox H. There are n s stores allocated for the storage of hazard scoresduring the path investigations; their contents are all reset to zero atthe beginning of each computation cycle. Using the notation H(p) torepresent the address of the pth one of these stores, the hazard scoreobtained for the segment is stored in the address H(n.r l a,). Forexample if the hazard score for the third segment of a path has justbeen calculated, it will be stored in the address H(2n a;,) where a willhave the value corresponding to the particular arc or manoeuvre whichhas been considered.

As indicated by box H the computer also examines the order of thecurrent segment, that is the suffix r of the last non-zero pathparameter. If the segment was the sth segment, that is the last segmentof a completed path, the next operation is as indicated by box .I. If itis not the sth segment, the next operation is as indicated by box Bagain, where the computer takes as the next starting point coordinatesfor consideration those held in the (r l)th SPC store, which are (X,,Y,, (1),), the coordinates of the end of the acceptable manoeuvre.

If the starting points of each successive segment have storms lyingwithin a predetermined distance of the most direct path from them to thedesired track and the manoeuvres considered for each segment in turn areacceptable and within the hazard limit, eventually an sth segment willbe examined. After the hazard score associated with that particular sthsegment has been put in the address H(n.s l a in the operationrepresentd by box H, the computer will examine the order of the currentsegment, and it will find it is an sth segment and the next operationwill thus be as indicated by box J. In box J the hazard scores of eachof the s segments of that complete path are summed. Since, in theoperation represented by box C or box K the computer has been updatingthe values of a a a, to correspond to the choice of manoeuvre for thefirst segment, choice of manoeuvre for the second segment choice ofmanoeuvre for the sth segment, respectively, the completed path is fullydefined by the current values of a a 11,. The addresses of the hazardscores associated with each segment of the path defined are thus easilyobtained. The value of a stored in the computer is the value of a, inthe address of the hazard score associated with the first segment. Thevalue of a 2 is the value of a, in the address of the hazard scoreassociated with the second segment and so on. For the first segment 2 0.For the second segment r l l and so on. Hence from (1) above the addressof the hazard score associated with the first segment is,

the address of the hazard score associated with the second segment is,

and so on. Thus, by summing the hazard scores stored in the addressesassociated with all the segments defining the path a total hazard scoreT for that path is found, which will be an integer in the range 0 to N;thus where (H (a,)) indicates the contents of the store H t)- Theoperation in box J may alternatively be initiated when the action of boxB finds that there are not further storms ahead of the starting pointco-ordinates under consideration, that is when the path segments alreadyconsidered though fewer than s will suffice to take the aircraft pastall of the storms. In this caee the summation required to derive thetotal hazard score will clearly be shortened to r terms.

The penalty score P associated with the completed path is then computedin a prescribed manner to form an indication of any economicdisadvantages of the path. For instance the penalty score may bedirectly proportional to the length of any detour involved. P is anintegral number within the limits 0 to N, and the greater the value of Pthe greater the associated penalty it represents.

In the computer a set of stores R is allocated for storing the totalhazards associated with fully investigated paths and a set of stores Vis allocated for storing the path parameters associated with these totalhazards. The integral value of P associated with any path is used as astore identification suffix to he stores R and V. Thus there are (N 1),Rp stores and (N l), Vp stores. As indicated by Box J the total hazardscore T for any potentially useful path having a penalty score P will becompared with the total hazard score previously entered in the store Rp;if and only if the score T is less than any score previously entered inthe store Rp, T will be entered in Rp replacing its previous contents.When this occurs the path parameters associated with the relevant pathwill then be entered in the corresponding Vp store, replacing anyprevious contents of the Vp store. This process eliminates some lessadvantageous paths from further consideration. At the start of acomputation cycle, an intolerably high hazard score value is inserted ineach of the relevant R stores. The comparison with T and any consequententries in the Rp and Vp stores will complete the action in respect ofthat particular path for the time being, and the programme goes into theoperation of box K again to start the consideration of the nextalternative path.

When all the paths have been considered, box D will be reached with allthe path parameters returned to zero. At this stage the total hazardscores and path parameters for the most advantageous paths will havebeen entered into the appropriate Rp and Vp stores. As indicated in boxL,- and box M, the programme then examines the contents of the Rp storesin the sequence, R R R R thereby considering the acceptable paths inorder of increasing penalties. It can print out or display the values ofP and T for the first Rp store found to contain a total hazard score Twhich is less than a prescribed value T and the values of P and T forthe first Rp store found to contain a total hazard score T less than asecond prescribed value T lower than T,. Alternatively or additionallyit can form another list comprising the values of P and T for each pathwhich is found to have a total hazard score less than the least of thetotal hazard scores found earlier in the sequence ofconsideration of theRp stores (which will relate to paths with lesser penalty scores). Thisprocess eliminates some paths which would involve a greater economicpenalty without gaining a reduction in hazard score, and retains detailsof a selection of advantageous paths. The path parameters a a,associated with any hazard selected from an Rp store are obtained fromthe orresponding Vp store and are simultaneously printed out ordisplayed with the P and T values. The storm pattern and the selectedpaths can then be displayed with their scores P and T on the display 13.The scores P and T for each selected path can be summed, and the pathhaving the least value of (P T) can be particularly identified.

The computation of the penalty score indicated in box J makes anallowance for incomplete paths, that is to say paths that have at leastone zero-valued path parameter. Such incomplete paths can be subjectedto the operation indicated by box J whenever it is found that thestarting point co-ordinates of a segment of order less than s, is foundto have no storms ahead of it in the operation as indicated in box B.Such paths, and paths ending off the desired track as hereinbeforedescribed with reference to FIG. 2, will require to be completed by afurther probably S-shaped path leading in a convenient and practicalmanner back to the desired track. While such further paths may, for thepurpose of completing the penalty score calculations, be assumed to behazard free, they may involve additional penalty score contributionswhich may be included in the penalty computation indicated in box J.

In FIG. 4 (including FIGS. 4a and 4b) the flow chart of P16. 3 has beenexpanded to show one way in which the effect of the wind speed anddirection on the storms under consideration can be taken into accountwhen computing the hazard scores for the various paths in a preferredform of the process described hereinabove. For brevity the descriptionof the operation indicated by a particular box has been omitted in FIG.4 where that box and its operation are common to the modes of operationshown by both FIG. 3 and FIG. 4.

As indicated by box A the coordinates of each storm in the storm list ascompiled in the operation of box A are modified, effectively by a shiftof origin of the coordinate system in the wind direction by an amountproportional to the wind speed. A second storm list is thus compiled,representing expected areas of turbulence downwind from the stormcenters indicated by the weather radar. This second storm list ishereinafter called the phantom storm list to distinguish it from thelist of real storm centers.

As indicated by box B and G the operations carried out by the computerwith respect to the phantom storm list are similar to those carried outwith respect to the real storm centers indicated by boxes B and G respectively. For any starting point considered in box B, the computerdetermines whether there are any real storms between that point and thedesired track, and if there are none in box B it makes a similardetermination with respect to the phantom storms. If there are no stormsahead as determined by box B and box B, the next operation is asdescribed hereinabove with reference to box J. If either box B or box Boperations indicate storms ahead then the next operation is as describedhereinabove with reference to box C.

Similarly if a particular choice of manoeuvre under consideration for aparticular segment does not exceed the limits as defined by theoperation indicated in box F with respect to an unacceptable detour or ahazardous final approach to a storm, then the next operation asdescribed hereinabove is as indicated by box G. Here the relevant partof the real storm list is selected and the hazard contribution to thatmanoeuvre by each of the selected real storms is computed and summed. Ifthe total hazard score for that manoeuvre is not excessive a similaroperation is carried out with respect to the phantom storm list, asindicated by box G. However, the hazard contribution summation operationin box G includes any total hazard contribution previously computed inbox G with respect to the real storms selected. If the total hazardcontribution of both real and phantom storms to that particularmanoeuvre is still not excessive, the next operation is as describedhereinabove with respect to box H. If the total hazard contribution ofeither the real storms or the real storms and the phantom storms isexcessive then the next operation is as described hereinabove withrespect to box K.

In the modified computer operation shown in FIG. 4, the hazardcontribution at any point in a proposed path due to a phantom storm agiven distance from that point need not necessarily be arranged to equalthe hazard contribution at that same point due to a real storm at thesame distance. Preferably the hazard contribution as a function ofdistance from a phantom storm is arranged to give predetermined lowerhazard contributions at all points than the corresponding hazardcontributions due to a real storm, to reflect the estimated decay of thestorm intensity in the downwind direction.

Many variations of the path selection process will suggest themselves toa skilled computer programmer. For example all n alternative manoeuvresfor the first segment might be examined before proceeding to the secondsegment alternatives and so on, or alternatively the manoeuvres for eachsegment leading to the least devious path might be examined firstfollowed by an examination of paths of increasing diversion from thedesired route.

The time interval between the input of successive sets of signalsrepresenting the locations of storm centers at a given instant of time,may be controlled by a timing circuit which might form part of thecomputer 8. This time interval may be chosen to allow sufficient timefor the computer 8 to complete and plot out the various selected pathsthrough the previous set of storm centers, or it may be chosen to allowthe aircraft sufficient time to fly one or more of the segments computedbefore presenting the pilot with more flight path information.

The height and elevation of storm centers might be further factors indetermining the hazard value to be assigned to each storm center. Thehazard value associated with each storm center might also be partlydetermined by the intensity of the received signal representing thatstorm or the distance that a given path under examination travelsthrough an area of given storm intensity.

It is emphasized that FIGS. 3 and 4 illustrate only one possiblesequence of computer programme operations suitable for selecting thedesired paths. Clearly there will be many possible variations of theactual programme devised, due to (a) variations in the skill ofindividual programmers, (b) the variety of types of computer for whichthe programme is to be written and (c) the different applications towhich the path selection is to be applied, for example in a ship borneapplication the hazard law would be different since the relative speedsand proximity to other ships land masses etc (the hazards to the ship)will be different from the hazards in an air borne application.

In an airborne application the computer might conveniently be a part ofthe Flight Management Computer conventionally installed in manyaircraft, or it might form part of the Navigational Computer and sharethe total computation time available to that computer.

If there are legal or political restrictions on the flight path, theycan be taken into account by adding to the storm list a set of imaginarystorms disposed along the boundary of the forbidden area. Clearly thesystem could also be developed to take account of other hazards, such asother aircraft for instance.

I claim:

1. Navigational apparatus for use in a moving vehicle, comprising ahazard indicating means for providing signals representing the locationof hazards with respect to the position of said hazard indicating means,said hazard indicating means being operative to provide signalsrepresenting the locations of a plurality of hazards, and computer meansconnected to receive the said signals from the hazard indicating meansand programmed for the computation of parameters which define at leastone distinct path substantially avoiding said plurality of hazards, saidcomputer means including means for providing signal outputs representingthe computed parameters.

2. Navigational apparatus as claimed in claim 1 wherein the hazardindicating means includes a weather radar means for locating stormcenters.

3. Navigational apparatus as claimed in claim 1 wherein the computermeans is programmed to provide program steps operative to consider aplurality of possible paths in sequence, the program including steps forrejecting any pathe found to involve more than a predetermined measureof risk, and the program also includ ing program steps for calculatinghazard scores and penalty scores for the paths not rejected.

4. Navigational apparatus as claimed in claim 3 wherein the computermeans is programmed to provide program steps which select and indicatethe parameters of paths having the lowest penalty scores associated withvarious acceptable hazard scores.

5. Navigational apparatus as claimed in claim 1 wherein the computermeans is programmed to provide program steps operative to consider pathswhich are composed of arcuate segments of equal length, whereinconsecutive ones of said segments have a common tangent at theirjunction, wherein the radii of the arcuate segments are chosen from aplurality of predetermined radii, and wherein each path is representedby a set of parameters indicating the radii of its arcuate segments.

6. Navigational apparatus as claimed in claim 1 including visual displaymeans connected to the computer means for displaying a map-likerepresentation of the location of the hazards, said display means beingoperative to also display at least one path avoiding the hazards.

7. Navigational apparatus as claimed in claim 3 wherein said computermeans is programmed to provide steps operative to calculate a hazardscore for each unrejected path by summing contributions comprising acontribution for each hazard which is detected by said hazard indicatingmeans, said programmed computer being operative to calculate eachcontribution as a predetermined function of the nearest distance from ahazard to a point on the path being considered.

8. Navigational apparatus as claimed in claim 2 wherein the computer isprogrammed to provide program steps which make an allowance for theeffect of the prevailing wind on the distribution of turbulenceassociated with each storm center by deriving a list of notional stormcenters having locations downwind from the actual storm centers, saidprogrammed computer being operative to treat said notional storm centersas additional hazards.

1. Navigational apparatus for use in a moving vehicle, comprising ahazard indicating means for providing signals representing the locationof hazards with respect to the position of said hazard indicating means,said hazard indicatIng means being operative to provide signalsrepresenting the locations of a plurality of hazards, and computer meansconnected to receive the said signals from the hazard indicating meansand programmed for the computation of parameters which define at leastone distinct path substantially avoiding said plurality of hazards, saidcomputer means including means for providing signal outputs representingthe computed parameters.
 2. Navigational apparatus as claimed in claim 1wherein the hazard indicating means includes a weather radar means forlocating storm centers.
 3. Navigational apparatus as claimed in claim 1wherein the computer means is programmed to provide program stepsoperative to consider a plurality of possible paths in sequence, theprogram including steps for rejecting any pathe found to involve morethan a predetermined measure of risk, and the program also includingprogram steps for calculating hazard scores and penalty scores for thepaths not rejected.
 4. Navigational apparatus as claimed in claim 3wherein the computer means is programmed to provide program steps whichselect and indicate the parameters of paths having the lowest penaltyscores associated with various acceptable hazard scores.
 5. Navigationalapparatus as claimed in claim 1 wherein the computer means is programmedto provide program steps operative to consider paths which are composedof arcuate segments of equal length, wherein consecutive ones of saidsegments have a common tangent at their junction, wherein the radii ofthe arcuate segments are chosen from a plurality of predetermined radii,and wherein each path is represented by a set of parameters indicatingthe radii of its arcuate segments.
 6. Navigational apparatus as claimedin claim 1 including visual display means connected to the computermeans for displaying a map-like representation of the location of thehazards, said display means being operative to also display at least onepath avoiding the hazards.
 7. Navigational apparatus as claimed in claim3 wherein said computer means is programmed to provide steps operativeto calculate a hazard score for each unrejected path by summingcontributions comprising a contribution for each hazard which isdetected by said hazard indicating means, said programmed computer beingoperative to calculate each contribution as a predetermined function ofthe nearest distance from a hazard to a point on the path beingconsidered.
 8. Navigational apparatus as claimed in claim 2 wherein thecomputer is programmed to provide program steps which make an allowancefor the effect of the prevailing wind on the distribution of turbulenceassociated with each storm center by deriving a list of notional stormcenters having locations downwind from the actual storm centers, saidprogrammed computer being operative to treat said notional storm centersas additional hazards.